Mouse B cells lacking NFATc1 exhibit defective proliferation, survival, isotype class switching, cytokine production, and T cell help.

NFAT transcription factors control the proliferation and survival of peripheral lymphocytes. We have reported previously that the short isoform NFATc1/αA whose generation is induced by immune receptor stimulation supports the proliferation and inhibits the activation-induced cell death of peripheral T and B cells. We will show in this study that in novel bacterial artificial chromosome transgenic mice that express EGFP under the control of entire Nfatc1 locus the Nfatc1/Egfp transgene is expressed as early as in double-negative thymocytes and in nonstimulated peripheral T and B cells. Upon immune receptor stimulation, Nfatc1/Egfp expression is elevated in B, Th1, and Th2 cells, but only weakly in T regulatory, Th9, and Th17 cells in vitro whose generation is affected by TGFβ. In naive lymphocytes, persistent immune receptor signals led to a 3–5 increase in NFATc1/αA RNA levels during primary and secondary stimulation, but a much stronger induction was observed at the protein level. Whereas anti-CD3+CD28 stimulation of primary T cells induces both NFATc1/αA and their proliferation and survival, anti-IgM stimulation of B cells induces NFATc1/αA and proliferation, but activation-induced cell death after 3-d incubation in vitro. The anti-IgM–mediated activation-induced cell death induction of B cells in vitro is suppressed by anti-CD40–, LPS-, and CpG-mediated signals. In addition to inducing NF-κB factors, together with anti-IgM, these signals also support the generation of NFATc1/αA. According to these data and the architecture of its promoter region, the Nfatc1 gene resembles a primary response gene whose induction is affected at the posttranscriptional level.

Epicutaneous application of Aldara cream containing the TLR7 agonist imiquimod (IMQ) to mice induces skin inflammation that exhibits many aspects of psoriasis, an inflammatory human skin disease. Here we show that mice depleted of B cells or bearing interleukin (IL)-10-deficient B cells show a fulminant inflammation upon IMQ exposure, whereas ablation of NFATc1 in B cells results in a suppression of Aldara-induced inflammation. In vitro, IMQ induces the proliferation and IL-10 expression by B cells that is blocked by BCR signals inducing NFATc1. By binding to HDAC1, a transcriptional repressor, and to an intronic site of the Il10 gene, NFATc1 suppresses IL-10 expression that dampens the production of tumour necrosis factor-α and IL-17 by T cells. These data indicate a close link between NFATc1 and IL-10 expression in B cells and suggest NFATc1 and, in particular, its inducible short isoform, NFATc1/αA, as a potential target to treat human psoriasis.

In peripheral lymphocytes, the transcription factors (TFs) NF-κB, NFAT, and AP-1 are the prime targets of signals that emerge from immune receptors. Upon activation, these TFs induce gene networks that orchestrate the growth, expansion, and effector function of peripheral lymphocytes. NFAT and NF-κB factors share several properties, such as a similar mode of induction and architecture in their DNA-binding domain, and there is a subgroup of κB-like DNA promoter motifs that are bound by both types of TFs. However, unlike NFAT and AP-1 factors that interact and collaborate in binding to DNA, NFAT, and NF-κB seem neither to interact nor to collaborate. We show here that NF-κB1/p50 and c-Rel, the most prominent NF-κB proteins in BCR-induced splenic B cells, control the induction of NFATc1/αA, a prominent short NFATc1 isoform. In part, this is mediated through two composite κB/NFAT-binding sites in the inducible Nfatc1 P1 promoter that directs the induction of NFATc1/αA by BCR signals. In concert with coreceptor signals that induce NF-κB factors, BCR signaling induces a persistent generation of NFATc1/αA. These data suggest a tight connection between NFATc1 and NF-κB induction in B lymphocytes contributing to the effector function of peripheral B cells. Keywords:Chromatin r Induction r Lymphocytes r Nfatc1 gene r NF-κB r Transcription Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionUpon Ag contact, the induction of resting peripheral lymphocytes leads to networks of signaling events that emerge from their Correspondence: Prof. Edgar Serfling e-mail: serfling.e@mail.uni-wuerzburg.de immune receptors. Primary targets of these signals are members of NF-κB, NFAT, and AP-1/ATF/CREB families of transcription factors (TFs). Upon activation they bind to the promoters, enhancers, and further regulatory elements of numerous genes, * These authors contributed equally to this work.C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2014. 44: 3392-3402 Molecular immunology 3393 control their expression and, thereby, orchestrate gene expression programs that control the growth, proliferation, and effector function of peripheral lymphocytes. One of the best-characterized lymphocyte-specific promoters is the promoter of human and murine Il2 genes. Within the Il2 promoter of approximately 300 bp, there are several noncanonical sequence motifs for the binding of NF-κB and AP-1/ATF/CREB factors, and composite NFAT + AP-1 sites to which both factors can bind with high affinity [1]. The distal NFAT-binding site from the Il2 promoter (the ARRE2 [2], or distal purine box, Pu-b d [3], that is often referred as the "prototypical" NFAT site), consists of the NFAT "core motif" 5 T / A GGAAAA 3 and a noncanonical TRE (TPA-responsive element), i.e. an AP-1/ATF-binding motif, located 10 bp downstream. Such composite NFAT + AP-1 sites are typical for the promoters/enhancers of many genes induced in peripheral T lymphocytes by immune rec...